Method of making light weight concrete of high strength



trco mrosulcflsf m commeoa PLASTIC. Exam fl c, se rates 2 A 2, 1935 ?I996,4'52

METHOD OF MAKING LIGHT WEIGHT coN- r CRETE OF HIGH STRENGTH 5 Q 7, s J

Erik B. Bjorkman, Montreal, Quebec, Canada No Drawing. Application July 10, 1933, Serial' No. 679,714. In Canada July 15, 1932 2 Claims. (Cl. 106-24) My invention relates to the production of conduce a concrete that is fully equal in qua1ities crete of low weight and high insulation value with that made from sufi'spec'ially manufacwhich is particularly intended for use inthe contured pcgmagggggtes at a price that is mastruction of high buildings, in which the reducterially lower, by mascara the fact that the ag- 5 tion of the dead weight of the structure is a matgregate employed may be produced at a very low 5 ter of great importance. cost. For this purpose I make use of an aggre- The modern trend in building construction togate produced by treating molte'rTblastfurnace wards increased height of the structures and s ag 1n suc u a v o o: higher demand for fireproofness, necessitating resembling the porous aggregate made b burn- 10 increased use of concrete in columns, floor arches, ingplay or shale is ofitamfi. 10 etc. has led to a tremendous increase in the ab- I Elast furnace slag, as is well known, is a bysolute weight of the buildings. As a consequence prodh'tdftlififfi'nufacture of pig-iron. Conthereof the expenditures on foundation work and siderable quantities of slag are formed in the on the carrying frame are very high, and the deprocess of smelting iron from the ore, and the dismand for greatest possible saving in the dead posal of this slag has heretofore generally been 15 weight, wherever such saving may be made, has an item of expense to the steel industry. Therearisen. Particular attention has been directed fore, it may as a rule be obtained at a very low towards the possibilities of decrgasigig llggjgm- Price.

paragimly h gjflglfi gg ordinary concrete by ,Attempts have been made heretofore to find 7 using lightag; egates and by assuage??? uses for blast furnace slag as concrete aggregate. 20

- 3 p'aifiiixi'g the e. atter 'methuw'in- Forinstance, by letting the molten slag slowly v'olves chemical and mechanical problems'of often cool and solidify, and by crushing and screening complicated nature, whereas the substitution of the resulting product, an aggregat'hssfiea obv lighter aggregates for heavier ones does not intained which has found extensive application in terfere with already established construction concrete manufacture instead of crushed rock or 25 methods, and therefore has been.widely employed gravel. Concrete made in this manner has apin order to lighten the volume weight of conproximately the same characteristics as ordinary crete. stone or gravel concrete, 1. e. it is substantially The mtcgnnnonly gmployed light 'nonrogs and has approximately the saine cretg aggregate today is coal ashes or ensity as the latter, around 140 lbs. per cubic 36 which are waste products and consequen y foot. Therefore, the use of air-cooled slag in be obtained at low cost. From a technical viewconcrete manufacture does not lead to saving in point this material is far from satisfactory, howweight or improved insulation value.

, ever, as it is l a c k ing in streng tl and usually con- It has also been suggested to tains chemically active impurities of which sulthe re mtainedyhsnmltau wed 35 phur is most detrimental, as there is always a tg apowerful and much larger streamm danger that the 'sulphugwill cause corrosion of water, runnin gjfio wnfifiute. e sudden consteel reinforcement embedded in the concrete. Tact of thefioltefislag'with the cold water causes In order to eliminate this danger, as well as in the slag to solidify into porous granules which 40 order to provide a technically more satisfactory possess a certainTegY'iebl"iiiecha'fiicalstrength. 40

aggregate, methods have been developed accord- A sieve test of the product obtained by this mething to which a porous light weight aggregate may 0d of granulation will show that the granulate be Produced y ww incipient is so fine that practically all of its passes through intumescence. grgductlhuaohtamzmsggan 8 mesh sieve i. e. it corresponds'in article chanically strong an free from detrimental imsizeW 31 son.

pfirmmgg I mnhwn in the art of concrete manugravel or crushed stone normally employed facture the use of sand alone as aggregate does t i an n J t n e not result in concrete of satisfactory qualities. porous nature of this aggregate the weight of If two samples of concrete are made, one with {F G f 5 th'e'idncretr'ma'yfie considerably decreased sand only and the other with a properly graded from low, which may be seen from the fact that gravel or crushed stone, it will be found that the an expensive heating process has to be employed strength and permanence of the latter is far suin the production of the porous aggregate. perior, assuming that the conditions of manufac- 5 The object of the present invention is to proture are otherwise equal. Similarly, the use of 6 thereby, although the cost of such concrete is far mixture of sand and coarse aggregate, such as %A/vv the slag granulate produced by pouring molten slag into a stream of water, as aggregate in the manufacture of concrete, results in the production of a weak concrete that easily crumbles on the surface when exposed to the effect of changing weather conditions or mechanical wear. In order to get satisfactory strength it isnecessary whereby t e oncre e becomes high, and the saving in weight due to the use of a .ight aggregate is partially offset. Furthermore, n order to insure suflicient wgijgability cj the concrete slurry for cast-iii si'tu application in the construction of buildings, it is necessary to dd compamtiyclyamflmnlllate lto the mix than 5 required when other light weight aggregates, suc h as ci nders and burnt clay or shale, are used, q ii slcl isrcathumanities-i 2; .9 slag aggregate. As is well known in the art, the 'w5i'liabilityor flow of the concrete slurry is a factor of utmost importance in the practical application of the concrete. Unless the slurry fills every crevice of the formwork, the strength of the concrete structure becomes wholly independable and the success of the construction may be jeopardized. It is also well known, that the strength of concrete is directly dependent on the relation between the quantity of cement and the quantity of water in the mix, other conditions of manufacture being equal. The less water is used for a given quantity of cement, the stronger concrete is obtained, assuming that the concrete slurry still retains sufficient workability for placing in the forms. For these reasons, the necessity of using comparatively much water inconcrete made from slag aggregate of the type described in the foregoing constitutes a serious drawback in the use of this material. In order to eliminate the disadvantages referred to, I make use, in carrying my invention into effect, of an aggregate obtained by treating fiolten blast furnace slag in such a manner as pro uce a gran a e a is substantially composed of large particles having great mechanical strength.

Before proceeding to describe the novel method of granulation I employ, reference is made to the fact that when the molten slag is granulated according to the method described in the foregoing, the solidification of the slag into porous' particles is caused by the sudden chilling of a solid stre m of molten sla by its contact with cold water of vastly greater volume. As a res e c ing, the interior stresses developing in the solidified slag cause the same to break up into very small particles which naturally become soaked with water and emerge from the granulation chute commingled with water. The granulat y invention into ifect cont ins gmparatimlit- Y e roresmizranmaimn sssmele ssl- The main i rgqmhwa mation process is the simultaneous disinteggtign of the stream 0 s ag y mechanical means' and 06151111 and s'ol1'diiic'atl'6fi"o'f"tli'"di" ops of slag thysjpgmgd. Thereby, large strong and porous particles varying in size from 2, inches down to impalpable dust are'formed, and I have found the mechanical disintegration together with the chilling of the slag in the same operation a necessary condition for the production of such particles. If the slag stream is not broken up mechanically at the same time as it is chilled, the resulting granulate is either lacking in mm e a gstetrezmmm' s ag, or y means 0 revolving steel vanes operstrength or of such great fineness as to make it fl'r/ unsuited as concrete aggregate.

The granulation is brought about in a special machine which may be constructed in different ways, as long as facilities are provided for disintegration and chilling in one operation. One way of constructing the granulation machine is to provide a hull of iron against which the molten slag is thrown, either mea of M15! no ating in the path of the stream of molten slag, thereby disintegrating the slag and throwing it against the surrounding iron hull. air is used 1 m I I l I s 1ag, ,as .w1l,,and this action ma. 9; enfiancecl by letting the air blast carr or steam, and By spraying cold water on the iron hull. If revolving vanes are used to efiect the disintegration, the slag is chilled by spraying water on the same. The granulate emerging from the latter type of granulating machine contains up to 10% of water, which soon evaporates owing to the high temperature of the granulate. The product emerging from the former type of granulation machine is dry. By regulating the force of the air blast or the speed of the revolving vanes and the quantity of water sprayed on the molten slag, it is possible to vary the relative sizes of the resulting granules within certain limits. Substantially, however, the granulate emerging from the granulation machine is composed of the following grades of particles:

Percent of total by weight Approximate volume weight Grade Pounds per cubic foot It will be seen that, substantially, more than one half of the material is too coarse to pass through an 8 mesh sieve. The individual particles have great mechanical strength, although their degree of porosity is high and the volume weight of the material is remarkably low, on an average less than 40 lbs. per cubic foot for the mixed granulate. The particles of slag bcingimdgse to pass the 8 mesh sieve, i. e. having a larger diameter than anytime anQgapabIE orwimstalillihg grmsfiffifoi'crushing.

The molten slag having been turned into granulate as described, the next step in the production of concrete of light weight according to the invention has to do with the grading of the granulate so as to produce an aggregate of determinate and desired particle sizes. It is obvious that the ulate maybe mixed directly with W Eggs 5% and water and serve as aggregate in its natura form. I have found, however, that by e various o q u ments, I am able to materially increase th compressive strength of the fifiisfied concrete witl'lout increasiri its weiht and interulate and re-appo rtionfering with the workability of the concrete slurry. or this reason, the granulate emerging mm the granulation mill is subjected to a screening operation and separated into different grades. The particle size of the grades may of course vary for different types of concrete. Howeve I have .tLa blast ci -gm 1:; the chilling action of the air serves to solidify the COMPOSITIONS, COATING 0R PLASTIC.

found that generally the division of the granulate into the following grades of particles enables me to produce an aggregate by re-apportioning the different grades that answers particularly well to 5 practical requirements incidental to the production of light weight concrete:

Grade 1: Particles retained on the 2 mesh sieve.

Grade 2:' Coarse grade. Particles passing the 2 mesh sieve but retained on the 4 mesh sieve.

Grade 3: Medium coarse grade. Particles passing the 4 mesh sieve but retained on the 8 mesh sieve.

Grade 4: Fine grade. Particles passing the 8 mesh sieve.

Grade 1, composed of particles retained on the 2 mesh sieve, comprises generally only about 15% of the total by weight, and the individual particles vary greatly in size. In order to bring them to a uniform size they are run through a crusher that brings them down to the approximate size of the particles composing Grade 2. The crushed particles are again screened and distributed according to size in Grades 2-4.

An examination of the individual particles of the different grades will show that the particles retained on the 8 mesh sieve have considerable mechanical strength, particularly the particles retained on the 4 mesh sieve, and are also very light, whereas the fine particles composing Grade 4 are weaker and relatively heavy. This latter grade of particles resembles closely the product obtained when molten slag is granulated in running water, as described above.

Reference has been made to the fact that concrete, of any kind, that is made from a properly graded mixture of fine and coarse aggregates proves most satisfactory in regard to strength and permanence when set, as well as in regard to ease of placing the concrete slurry. Similarly, it will be found that concrete made from a properly graded mixture of fine and coarse slag a gregate w l djis fiiiesla'g" only, conditions Hfma'nufactrire' being otherwise equal. I have found, however, that if the same relative proportions of fine and coarse slag aggregate are used, as is common in making concrete from ordinary sand and gravel or crushed stone, the comparatively low mechanical strength of the particles composing the fine grade affects the strength appreciably. it is desira s ag ag regat which of course may be done bTsfiBs ituting orgilialliandfor part or all of the fine slag. Although the strength of the concrete will be increased thereby, it is obvious that the density will also increase, in view of the fact that ordinary sand weighs considerably more than the fine slag aggregate.

It is well known that fine aggregates in general serve as a medium between the exceedingly fine cement particles and the coarse aggregate. For a definite cement content and water-cement ratio, changes in the proportion of fine compared to coarse aggregates will lead to "changes in the workability of the concrete slurry. When the proportion of fine aggregate is decreased, the concrete slurry becomes gritty, to the detriment of the ultimate strength of the concrete, unless the decrease in fine aggregate is offset by a corresponding increase in the proportion of cement. It is obvious that the more cement is used in the mix, the more costly the concrete becomes.

the concrete will notidiifiefgreatly. In fact, I

I have found that the disadvantages referred to may be overcome by rinding part of the grad of slag passing the 8 mesHsieve to cegne nl ness and adding thereof to the mix, e reater. relative l o. 'clesthus v ob ained enables me t increase t e quan-- tity of coarse aggregate without changing the workability of the co r b mae .1..- mm withou mcreas' 1 ensit b reason of the t ion 0 gro J o a q in consequence the eof, n -porous slag particles, oreqyer ngg ks 'i'fimfifimfimggimn enpwinzwm thelargfiiro fidffigg of strogregata particlesfbfif'the finely ground slag particles t e ew a sri i liwilm esamesszc 0 miles It gg iq iil .ce zaLeeracles- T s importafitresult is due to the fact that granulated blast furnace slag is, from a chemical viewpoint, substantially the same composite material as Portland cement, although deficient in lime. Redlw @ihLfinenessnLPQlfllllQEm it shows great hydraulic activity, provided thefiefiaeireyifinfiieisadufitractea by 'the firericiajaf free'jm i isome'fofm'fiftliemixr'whenground slag is mixed withPbi'tlaiid'cEneht and water, such free lime is provided, by reason of the fact that the Portland cement itself contains chemically active free lime. The action of the lime in the Portland cement may of course be further enhanced by adding a small quantity of hydrated lime to the mix, although as a rule satisfactory setting action takes place in th'e'slag 1 121191111. uefiad fisg tmT "I-Iaving separated the granulate into grades, as pointed out, I therefore grind part of the grade of particles passing the 8 mesh sieve to cement fineness, and add the ground slag to the concrete mix. I have found that as long as the weight of the ground slag does not exgggg 252, of the weight 0 e ortland cement the effec of tHe addition or the slag on the strength will be practically the same as if Portland cement in equal amounts had been added. If more than 25% of ground slag by weight of the Portland cement is added, the hardening of the concrete in the early stages is slower than if equal amounts of Portland cement were added instead of the ground slag, although the ultjmate strength of have found-'tliatas'rnuch as 70% of gm ,9 fihlsitaeize ieatmar.kelsiselgad. nu maimesameultiggtegtren monhe cnncreteasiuttainedi hemeqnalamomatsmf er l e w a su sislsgleeieas cointhem By adding slag ground to the fineness 01' eement to the mix, as described, I am able to decrease the proportion of the fine grade of the mix to such an extent, that substitution of ordinary sand for the fine grade of slagaggregate may be done without materially increasing the volume weight or density of the concrete. The sand having greater mechanical strength than the fine slag, 'as pointed out, I am thus able to produce a concrete of substantially the same ultimate compressive strength as ordinary concrete, made with said and gravel or crushed rock as aggregates, the quantity of Portland cement employed in the mix and the workability of the concrete slurry being the same in both cases. This important result is due to the fact Examine? that, although the coarse slag particles have less rock particles, the setting action in the finely ground slag makes up for the loss in strength incurred bfihe use of amaggregate. Concrete produced inthis manner weighs approximately 40% less than ordinary concrete, in wh as aggregates.

It should be noted that the operation of reducing the slag particles passing'the 8 mesh sieve to cement fineness involves no considerable expense, as the particles already are very fine and are easily ground. The pulverized slag may be transported as any other aggregate, asit is practically inert even in the presence of moisture, unless chemically active free lime or other free bases are also present. Preferably the ground slag is re-mixed with the other grades 20 :of aggregate at the plant where it is prepared, 1 and delivered to the user in this form.

Concrete suitable for structural purposes may "be made by mixing part by weight of Portland cement, part of ground slag, 1% parts of aggregate (Grade an coarse slag aggregate (Grade 2). With a water-cement ra o o .8 bs. water per- 1 lb. of Portland cement, the slump of the concrete slurry will be approximately inches, as measured according to standard methods. The concrete will attain a compressive strength in excess of 2500 lbs. er square inch at the age of 28 days, and will weigh less than 100 l f ot in air condition.

For non-structural purposes, such as floor fill and similar applications, for which low weight J and high insulation value of the concrete are more important qualities than high strength, the concrete mix may preferably be composed of 1 part of Portland cement by weight, 1 part of ground slag, 2 parts of fine slag aggregate (Grade 4), 2 parts of medium coarse slag aggregate (Grade 3), and 3 parts of coarse slag aggregate (Grade 2). ,This mix requires 2 lbs. of water per lb. of Portland cement for a comparatively dry consistency, such as is usually in placing concrete fills. The density of this concrete in air dry condition is only around '70 lbs. per cubic foot, and it is therefore highly resistant against the transmission of heat and sound.

The foregoing recommendations as to the proportion of cement, aggregate and water will serve to give a general outline of satisfactory concrete mixes from two different fields of application. It is obvious, that the proportions of the various ingredients may be varied to produce concrete of specific requirements. By reason of the fact, that the admixture of finely ground slag in the aggregate, acting as Portland cement in the process of hardening and thus increasing the strength, also makes it possible to employ a large proportion of coarse aggregate particles of great mechanical strength, concrete produced as described will attain considerably higher compressive strength for a given density than any light weight concrete heretofore made from blast furnace slag, or mixtures of blast furnace slag and ordinary sand, or, in fact, from any light weight aggregate. Furthermore, the qualities of concrete made according to the invention are fully equal with, or in fact, superior to those of light weight concrete made from Portland cement, water and aggregates specially manufactured by burning clay or shale to incipient fusion. The cost of the latter type of concrete is quite appreciably higher, as will be seen from the fact that the aggregate employed in its manufacture is prepared by first procuring the raw material, clay or shale, and then heating the same to a very high temperature, whereas the aggregate I employ in carrying my invention into effect is made by chilling the molten slag, which is a by-product of little or no value, the'disposal of which generally constitutes an additional item of cost incidental to the manufacture of pigiron.

Although concrete produced according to this invention is primarily intended for cast-in-situ construction, it has also proved very satisfactory for the manufacture of pre-cast units, particularly structural reinforced slabs for which concrete of high strength is required.

Owing to the porous nature of the aggregate,

has, i. e. the more air cells are trapped in its interior, the higher its resistance against the transmission of both heat and sound will be. For this reason, concrete'made according to the invention is eminently suitable for the construction of fioors according to standardized engineering practice. Such fioors consist of. a load-bearing slab of structural concrete and a fill of non-structural concrete serving as an insulating medium, transmission of sound. Both the load-bearing slab and the fill may be constructed in concrete according to this invention, whereby an exceedingly light and sound-insulating fioor is obtained. Having thus described my invention, what I claim is: v

1. The herein described method of making cast-in-situ concrete of lower weight than 115 pounds per cubic foot and substantially the same strength as that of normal heavy concrete containing equal proportion of Portland cement per unit volume, which comprises mechanically disintegrating a stream of molten blast furnace slag into drops of molten slag and chilling the drops to produce a granulate consisting of hard porous particles, separating said granulate into grades of particles of determinate and desired sizes, reducing the size of particles having larger diameter than substantially one half of an inch by crushing, reducing part of the grade of particles having smaller diameter than substantially one eighth of an inch to the fineness of particularly against the Portland cement by grinding, adding the ground slag to the remainder of said grade in desired proportions, re-apportioning the grades into an aggregate composed of particles having smaller diameter than substantially one half of an inch, mixing said aggregate with Portland cement and water, and allowing the mixture to set.

2. The herein described method of making cast-in-situ concrete of lower weight than 115 pounds per cubic foot and substantially the same strength as that of normal heavy concrete containing equal proportion of Portland cement per unit volume as claimed in claim 1, with the addition of sand to the mixture of blast furnace slag, Portland cement and water.

ERIK B. BJORKMAN. 

